Butadiene is used as an intermediate product in many petrochemical products in the petrochemical market and, as one of the most important basic fractions in the current petrochemical market, the demand for butadiene and value thereof are steadily increasing.
Methods for producing butadiene include an extraction method from C4 fraction through naphtha cracking, direct dehydrogenation of normal-butene (n-butene), oxidative dehydrogenation of n-butene, etc. However, the production method through naphtha cracking, which is responsible for at least 90% of the butadiene that is introduced on the market, not only has a high energy consumption due to a high reaction temperature, but is also not a dedicated process for processing only butadiene, and thus has a limitation in that basic fractions that are other than butadiene are produced as surplus. In addition, the production method through direct dehydrogenation of normal-butene is not only thermodynamically disadvantageous, but, as an endothermic reaction, requires conditions of high temperature and low pressure in order to produce a high yield of butadiene, and thus is not appropriate in a commercial process for producing butadiene.
Meanwhile, the production method through oxidative dehydrogenation of normal-butene, which uses a reaction that produces butadiene by using oxygen as a reactant to remove two hydrogens from normal-butene, is very advantageous thermodynamically because stable water is produced as a reaction product, and unlike the direct dehydrogenation reaction, is an exothermic reaction. Thus a high yield of butadiene may be obtained at a lower temperature than the direct dehydrogenation reaction. Consequently, the method of producing butadiene through the oxidative dehydrogenation of normal-butene may be an effective production process that is capable of meeting the increasing demand for butadiene.
In such the method for producing butadiene through oxidative dehydrogenation of normal-butene, nitrogen, steam, etc., which are other than the reactants (normal-butene and oxygen), are introduced in order to reduce the danger of explosion, and also to prevent coking of catalyst and remove the heat of reaction. Here, along with butadiene, which is the primary product, carbon monoxide, carbon dioxide, etc., which are byproducts, are secondarily produced, and among the byproducts, carbon monoxide, etc. must be separated and discharged in order to prevent a continuous build up in the process. However, there is a limitation in that, during the discharging, active components, such as oxygen, unreacted raw material (normal-butene), and the produced butadiene, are discharged along with the byproducts to outside of the system.
Typically, air is used as an input source for oxygen (O2) and nitrogen (N2) in the oxidative dehydrogenation reaction, and here, there is a limitation in it being difficult to arbitrarily control an amount of the active components, such as nitrogen, oxygen, unreacted raw material, and butadiene, that are discharged. Therefore, a method is needed that is capable of minimizing the active components that are discharged.